Thermoelectric conversion device, method for controlling thermoelectric conversion device, method for cooling and/or heating object by using thermoelectric conversion device, and electronic device

ABSTRACT

A thermoelectric conversion device includes: a first thermoelectric conversion module, a first insulating layer, and a second thermoelectric conversion module. The first (second) thermoelectric conversion module includes one or two or more thermoelectric conversion elements, a first (third) connection electrode, and a second (fourth) connection electrode. The thermoelectric conversion elements of the first (second) thermoelectric conversion module are electrically connected to the first (third) connection electrode and the second (fourth) connection electrode and located on an electric path connecting these connection electrodes. Each of the thermoelectric conversion elements includes a thermoelectric converter. The thermoelectric converter of at least one of the thermoelectric conversion elements has a phononic crystal layer having a phononic crystal structure including a plurality of regularly arranged through holes. A through direction of the plurality of through holes in this crystal structure is substantially parallel to a stacking direction of the first thermoelectric conversion module, the first insulating layer, and the second thermoelectric conversion module.

TECHNICAL FIELD

The present disclosure relates to a thermoelectric conversion device, amethod for controlling the thermoelectric conversion device, a methodfor cooling and/or heating an object using the thermoelectric conversiondevice, and an electronic device including the thermoelectric conversiondevice.

BACKGROUND ART

PTL 1, PTL 2, and NPL 1 disclose periodic structures including aplurality of through holes. In these periodic structures, the throughholes are regularly arranged in a thin film with a period of the orderof nanometers (in the range of 1 nm to 1000 nm) in plan view. Eachperiodic structure is one type of phononic crystal structure. Thephononic crystal structure of such a type generally has a unit cell thatis a minimum unit forming the arrangement of the through holes. Withthis phononic crystal structure, the thermal conductivity of the thinfilm can be reduced. The thermal conductivity of a thin film can bereduced also by, for example, porosification. This is because the poresintroduced into the thin film by the porosification reduce the thermalconductivity of the thin film. However, in the thin film having thephononic crystal structure, the thermal conductivity of the basematerial itself forming the thin film can be reduced. Therefore, it isexpected to further reduce the thermal conductivity of such a thin filmas compared with that achieved by simple porosification.

A thermoelectric conversion element including a thermoelectric convertercontaining a thermoelectric conversion material is a known art. The useof the thermoelectric conversion element allows a thermoelectricconversion device to be constructed. The thermoelectric conversiondevice can cool and/or heat an object by utilizing the Peltier effect.PTL 3 discloses a thermoelectric conversion element including a p-typethermoelectric conversion material and an n-type thermoelectricconversion material.

CITATION LIST Patent Literature

PTL 1: U.S. Patent Application Publication No. 2017/0047499

PTL 2: U.S. Patent Application Publication No. 2017/0069818

PTL 3: International Publication No. WO2011/048634

Non Patent Literature

NPL 1: Nomura et al., “Impeded thermal transport in Si multiscalehierarchical architectures with phononic crystal nanostructures”,Physical Review B 91, 205422 (2015)

SUMMARY OF INVENTION Technical Problem

The present disclosure provides a thermoelectric conversion device thatcan cool and/or heat an object with a high degree of flexibility and is,for example, suitable for maintaining variations in the temperature ofthe object within a prescribed range.

Solution to Problem

The present disclosure provides the following thermoelectric conversiondevice.

-   -   A thermoelectric conversion device including:    -   a first thermoelectric conversion module;    -   a first insulating layer disposed on the first thermoelectric        conversion module; and    -   a second thermoelectric conversion module disposed on the first        insulating layer,    -   wherein the first thermoelectric conversion module includes one        or two or more thermoelectric conversion elements, a first        connection electrode, and a second connection electrode,    -   wherein the thermoelectric conversion elements of the first        thermoelectric conversion module are electrically connected to        the first connection electrode and the second connection        electrode and located on an electric path connecting the first        connection electrode and the second connection electrode,    -   wherein the second thermoelectric conversion module includes one        or two or more thermoelectric conversion elements, a third        connection electrode, and a fourth connection electrode,    -   wherein the thermoelectric conversion elements of the second        thermoelectric conversion module are electrically connected to        the third connection electrode and the fourth connection        electrode and located on an electric path connecting the third        connection electrode and the fourth connection electrode,    -   wherein each of the thermoelectric conversion elements includes        a thermoelectric converter,    -   wherein the thermoelectric converter of at least one of the        thermoelectric conversion elements includes a phononic crystal        layer having a phononic crystal structure including a plurality        of regularly arranged through holes, and    -   wherein a through direction of the plurality of through holes in        the phononic crystal structure is substantially parallel to a        stacking direction of the first thermoelectric conversion        module, the first insulating layer, and the second        thermoelectric conversion module.

Advantageous Effects of Invention

The present disclosure can provide a thermoelectric conversion devicethat can cool and/or heat an object with a high degree of flexibilityand is, for example, suitable for maintaining variations in thetemperature of the object within a prescribed range.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view schematically showing an example of thethermoelectric conversion device of the present disclosure.

FIG. 2 is a cross-sectional view schematically showing an example of athermoelectric converter in a thermoelectric conversion element that thethermoelectric conversion device of the present disclosure can have.

FIG. 3 is a cross-sectional view schematically showing another exampleof the thermoelectric converter in the thermoelectric conversion elementthat the thermoelectric conversion device of the present disclosure canhave.

FIG. 4 is a plan view when the thermoelectric converter in FIG. 3 isviewed from a first phononic crystal layer side.

FIG. 5 is a plan view when the thermoelectric converter in FIG. 3 isviewed from a second phononic crystal layer side.

FIG. 6A is a schematic illustration showing an example of a unit cell ofa phononic crystal structure that the thermoelectric conversion elementcan have.

FIG. 6B is a schematic illustration showing another example of the unitcell of the phononic crystal structure that the thermoelectricconversion element can have.

FIG. 6C is a schematic illustration showing yet another example of theunit cell of the phononic crystal structure that the thermoelectricconversion element can have.

FIG. 6D is a schematic illustration showing still another example of theunit cell of the phononic crystal structure that the thermoelectricconversion element can have.

FIG. 7 is a plan view schematically showing an example of the phononiccrystal structure that the thermoelectric conversion element can have.

FIG. 8A is a schematic illustration showing a unit cell of a firstdomain included in the phononic crystal structure in FIG. 7 and theorientation of the unit cell.

FIG. 8B is a schematic illustration showing a unit cell of a seconddomain included in the phononic crystal structure in FIG. 7 and theorientation of the unit cell.

FIG. 9 is an enlarged view of region R1 in the phononic crystalstructure in FIG. 7.

FIG. 10 is a plan view schematically showing another example of thephononic crystal structure that the thermoelectric conversion elementcan have.

FIG. 11 is enlarged view of region R2 in the phononic crystal structurein FIG. 10.

FIG. 12 is a plan view schematically showing yet another example of thephononic crystal structure that the thermoelectric conversion elementcan have.

FIG. 13 is an enlarged view of region R3 in the phononic crystalstructure in FIG. 12.

FIG. 14 is a plan view schematically showing still another example ofthe phononic crystal structure that the thermoelectric conversionelement can have.

FIG. 15 is a plan view schematically showing even another example of thephononic crystal structure that the thermoelectric conversion elementcan have.

FIG. 16 is a plan view schematically showing even another example of thephononic crystal structure that the thermoelectric conversion elementcan have.

FIG. 17A is a schematic illustration showing an example of the unit cellof the phononic crystal structure that the thermoelectric conversionelement can have.

FIG. 17B is a schematic illustration showing another example of the unitcell of the phononic crystal structure that the thermoelectricconversion element can have.

FIG. 18 is a plan view schematically showing even another example of thephononic crystal structure that the thermoelectric conversion elementcan have.

FIG. 19 is a plan view schematically showing even another example of thephononic crystal structure that the thermoelectric conversion elementcan have.

FIG. 20A is a plan view schematically showing an example of the phononiccrystal layer that the thermoelectric conversion element can have.

FIG. 20B is a cross-sectional view showing a cross section 20B-20B ofthe phononic crystal layer in FIG. 20A.

FIG. 21 is a cross-sectional view schematically showing another exampleof the thermoelectric converter in the thermoelectric conversion elementthat the thermoelectric conversion device of the present disclosure canhave.

FIG. 22A is a plan view schematically showing another example of thephononic crystal layer that the thermoelectric conversion element canhave.

FIG. 22B is a cross-sectional view showing a cross section 22B-22B ofthe phononic crystal layer in FIG. 22A.

FIG. 23 is a cross-sectional view schematically showing another exampleof the thermoelectric converter in the thermoelectric conversion elementthat the thermoelectric conversion device of the present disclosure canhave.

FIG. 24A is a schematic cross-sectional view illustrating an example ofa method for producing the thermoelectric conversion element that thethermoelectric conversion device of the present disclosure can have.

FIG. 24B is a schematic cross-sectional view illustrating the example ofthe method for producing the thermoelectric conversion element that thethermoelectric conversion device of the present disclosure can have.

FIG. 24C is a schematic cross-sectional view illustrating the example ofthe method for producing the thermoelectric conversion element that thethermoelectric conversion device of the present disclosure can have.

FIG. 24D is a schematic cross-sectional view illustrating the example ofthe method for producing the thermoelectric conversion element that thethermoelectric conversion device of the present disclosure can have.

FIG. 24E is a schematic cross-sectional view illustrating the example ofthe method for producing the thermoelectric conversion element that thethermoelectric conversion device of the present disclosure can have.

FIG. 24F is a schematic cross-sectional view illustrating the example ofthe method for producing the thermoelectric conversion element that thethermoelectric conversion device of the present disclosure can have.

FIG. 24G is a schematic cross-sectional view illustrating the example ofthe method for producing the thermoelectric conversion element that thethermoelectric conversion device of the present disclosure can have.

FIG. 24H is a schematic cross-sectional view illustrating the example ofthe method for producing the thermoelectric conversion element that thethermoelectric conversion device of the present disclosure can have.

FIG. 24I is a schematic cross-sectional view illustrating the example ofthe method for producing the thermoelectric conversion element that thethermoelectric conversion device of the present disclosure can have.

FIG. 24J is a schematic cross-sectional view illustrating the example ofthe method for producing the thermoelectric conversion element that thethermoelectric conversion device of the present disclosure can have.

FIG. 24K is a schematic cross-sectional view illustrating the example ofthe method for producing the thermoelectric conversion element that thethermoelectric conversion device of the present disclosure can have.

FIG. 24L is a schematic cross-sectional view illustrating the example ofthe method for producing the thermoelectric conversion element that thethermoelectric conversion device of the present disclosure can have.

FIG. 24M is a schematic cross-sectional view illustrating the example ofthe method for producing the thermoelectric conversion element that thethermoelectric conversion device of the present disclosure can have.

FIG. 24N is a schematic cross-sectional view illustrating the example ofthe method for producing the thermoelectric conversion element that thethermoelectric conversion device of the present disclosure can have.

FIG. 24O is a schematic cross-sectional view illustrating the example ofthe method for producing the thermoelectric conversion element that thethermoelectric conversion device of the present disclosure can have.

FIG. 25 is a cross-sectional view schematically showing another exampleof the thermoelectric conversion device of the present disclosure.

FIG. 26 is a cross-sectional view schematically showing yet anotherexample of the thermoelectric conversion device of the presentdisclosure.

FIG. 27 is a flowchart showing an example of a control method in thepresent disclosure.

FIG. 28 is a graph showing voltage application patterns in an example ofthe control method in the present disclosure.

FIG. 29 is a graph showing voltage application patterns in an example ofthe control method in the present disclosure.

DESCRIPTION OF EMBODIMENTS (Findings Underlying the Present Disclosure)

The thermoelectric conversion device of the present disclosure includesa plurality of thermoelectric conversion modules stacked together. Thethermoelectric conversion modules can be controlled independentlythrough connection electrodes disposed in the respective thermoelectricconversion modules. For example, a thermoelectric conversion moduleclose to an object is controlled differently from a thermoelectricconversion module away from the object. In this manner, the degree offlexibility in controlling cooling and/or heating of the object can beincreased.

Moreover, the thermoelectric conversion device of the present disclosureincludes a thermoelectric conversion element including a thermoelectricconverter having a phononic crystal structure. This can enhance thethermal insulation performance of the thermoelectric conversion moduleseach including the above element, typically the thermal insulationperformance of the plurality of thermoelectric conversion modules intheir stacking direction. The enhanced thermal insulation performanceimproves the thermoelectric conversion efficiency of the thermoelectricconversion modules. The enhanced thermal insulation performance alsoimproves the degree of flexibility in control patterns forthermoelectric conversion modules adjacent to each other when thesemodules are controlled independently. These contribute synergisticallyto the improvement in the degree of flexibility in controlling thecooling and/or heating of the object.

(Embodiments of the Present Disclosure)

Embodiments of the present disclosure will be described with referenceto the drawings. The embodiments described below show general orspecific examples. Numerical values, shapes, materials, components,arrangements and connections of the components, process conditions,steps, the order of the steps, etc. shown in the following embodimentsare merely examples and are not intended to limit the presentdisclosure.

Among the components in the following embodiments, components notdescribed in an independent claim representing the broadest concept willbe described as optional components. The drawings are schematic drawingsand are not necessarily strictly accurate illustrations.

[Thermoelectric Conversion Device] FIRST EMBODIMENT

FIG. 1 shows a thermoelectric conversion device in a first embodiment.The thermoelectric conversion device 1 in FIG. 1 includes a firstthermoelectric conversion module 2, a first insulating layer 3, and asecond thermoelectric conversion module 4. The first insulating layer 3is disposed on the first thermoelectric conversion module 2. The secondthermoelectric conversion module 4 is disposed on the first insulatinglayer 3. The first thermoelectric conversion module 2, the firstinsulating layer 3, and the second thermoelectric conversion module 4each have a laminar shape and are stacked in this order to form alayered structure 5.

The first thermoelectric conversion module 2 includes two or morethermoelectric conversion elements 21(21 a), a first connectionelectrode 11, and a second connection electrode 12. The thermoelectricconversion elements 21 a of the first thermoelectric conversion module 2are electrically connected to the first connection electrode 11 and thesecond connection electrode 12. The electrical connection of eachthermoelectric conversion element 21 a to the first connection electrode11 or the second connection electrode 12 is a direct connection or anindirect connection through another thermoelectric conversion element 21a. The thermoelectric conversion elements 21 a are located on anelectric path connecting the first connection electrode 11 and thesecond connection electrode 12. In the example in FIG. 1, the two ormore thermoelectric conversion elements 21 a are electrically connectedto each other in series between the first connection electrode 11 andthe second connection electrode 12. However, the electrical connectionform of the thermoelectric conversion elements 21 a between the firstconnection electrode 11 and the second connection electrode 12 is notlimited to the above example. For example, a combination of series andparallel connections may be used. By applying a voltage through thefirst connection electrode 11 and the second connection electrode 12,the thermoelectric conversion elements 21 a and the first thermoelectricconversion module 2 operate as Peltier elements and a Peltier module,respectively. The Peltier module is, for example, a Peltier-type coolingmodule, a Peltier-type cooling/heating module, or a Peltier type heatingmodule.

The second thermoelectric conversion module 4 includes two or morethermoelectric conversion elements 21(21 b), a third connectionelectrode 13, and a fourth connection electrode 14. The thermoelectricconversion elements 21 b of the second thermoelectric conversion module4 are electrically connected to the third connection electrode 13 andthe fourth connection electrode 14. Each of the thermoelectricconversion elements 21 b is electrically connected to the thirdconnection electrode 13 or the fourth connection electrode 14 directlyor indirectly through another thermoelectric conversion element 21 b.The thermoelectric conversion elements 21 b are located on an electricpath connecting the third connection electrode 13 and the fourthconnection electrode 14. In the example in FIG. 1, the two or morethermoelectric conversion elements 21 b are electrically connected toeach other in series between the third connection electrode 13 and thefourth connection electrode 14. However, the electrical connection formof the thermoelectric conversion elements 21 b between the thirdconnection electrode 13 and the fourth connection electrode 14 is notlimited to the above example. For example, a combination of series andparallel connections may be used. By applying a voltage through thethird connection electrode 13 and the fourth connection electrode 14,the thermoelectric conversion elements 21 b and the secondthermoelectric conversion module 4 operate as Peltier elements and aPeltier module, respectively.

In each of the first thermoelectric conversion module 2 and the secondthermoelectric conversion module 4, the two or more thermoelectricconversion elements 21 are typically arranged in an array. The firstthermoelectric conversion module 2 and/or the second thermoelectricconversion module 4 may include one thermoelectric conversion element21.

The electrical connection form of the thermoelectric conversion elements21 in the first thermoelectric conversion module 2 may be the same as ordifferent from the electrical connection form of the thermoelectricconversion elements 21 in the second thermoelectric conversion module 4.

In the example in FIG. 1, the number of first connection electrodes 11,the number of second connection electrodes 12, the number of thirdconnection electrodes 13, and the number of fourth connection electrodes14 are each 1. However, the number of connection electrodes may be twoor more.

The voltage applied between the first connection electrode 11 and thesecond connection electrode 12 and the voltage applied between the thirdconnection electrode 13 and the fourth connection electrode 14 can becontrolled independently. This allows the first thermoelectricconversion module 2 and the second thermoelectric conversion module 4 tobe controlled independently. For example, a first voltage may be appliedto the first thermoelectric conversion module 2, and a second voltagewith an application pattern different from that of the first voltage maybe applied to the second thermoelectric conversion module 4.

The thermoelectric conversion device 1 in FIG. 1 further includes asubstrate (base layer) 6, a second insulating layer 7, and a protectivelayer 8. The layered structure 5 is disposed on the substrate 6 with thesecond insulating layer 7 therebetween. The protective layer 8 isdisposed on the second thermoelectric conversion module 4. Theprotective layer 8 is disposed as an outermost layer of thethermoelectric conversion device 1 (the outermost layer on the sideopposite to the substrate 6). The thermoelectric conversion device 1 hasa structure including the substrate 6, the second insulating layer 7,the first thermoelectric conversion module 2, the first insulating layer3, the second thermoelectric conversion module 4, and the protectivelayer 8 that have been stacked in this order. The first connectionelectrode 11, the second connection electrode 12, the third connectionelectrode 13, and the fourth connection electrode 14 are via linesembedded in through holes passing through the layer(s) and extending inthe stacking direction of the layered structure 5, reach the uppersurface of the protective layer 8, and are exposed at the upper surface.The exposed end of each of the connection electrodes can be, forexample, a connection point for a controller and/or a control modulethat controls the voltage applied to the first thermoelectric conversionmodule 2 or the second thermoelectric conversion module 4.

Each thermoelectric conversion element 21 includes a p-typethermoelectric converter 22 and an n-type thermoelectric converter 23that serve as thermoelectric converters and further includes a firstelectrode 24, a second electrode 25, and a third electrode 26. A firstend of the p-type thermoelectric converter 22 and a first end of then-type thermoelectric converter 23 are electrically connected throughthe first electrode 24. A second end of the p-type thermoelectricconverter 22 is electrically connected to the second electrode 25. Asecond end of the n-type thermoelectric converter 23 is electricallyconnected to the third electrode 26. One selected from the secondelectrode 25 and the third electrode 26 is disposed on the electric pathconnecting the corresponding connection electrodes and located on theupstream side in the path. The other selected from the second electrode25 and the third electrode 26 is disposed on the electric pathconnecting the corresponding connection electrodes and located on thedownstream side in the path.

In other words, a voltage can be applied to the thermoelectricconversion element 21 through the second electrode 25 and the thirdelectrode 26. The second electrode 25 of each of the thermoelectricconversion elements 21 a is electrically connected to the thirdelectrode of an adjacent one of the thermoelectric conversion elements21 a. The upstream and downstream sides in the electric path may bedetermined, for example, based on the direction of the electric currentflowing through the path when a typical voltage is applied to thethermoelectric conversion module. In each thermoelectric conversionelement 21, the direction in which a pair of electrodes sandwiching thethermoelectric converter therebetween are connected is generally thestacking direction of the layered structure 5. In other words, thedirection in which the flow of heat is controlled in the thermoelectricconversion elements 21 and the thermoelectric conversion device 1 isgenerally the stacking direction of the layered structure 5. In each ofthe thermoelectric conversion elements 21 in FIG. 1, an insulatingportion 27 is disposed between the p-type thermoelectric converter 22and the n-type thermoelectric converter 23, and this configurationallows electric insulation between the thermoelectric converters 22 and23 to be maintained.

The p-type thermoelectric converter 22 and/or the n-type thermoelectricconverter 23 in each thermoelectric conversion element 21, typicallyeach of the p-type thermoelectric converter 22 and the n-typethermoelectric converter 23, includes a phononic crystal layer. Thephononic crystal layer has a plurality of regularly arranged throughholes. The through direction of the plurality of through holes in thephononic crystal structure is substantially parallel to the stackingdirection of the layered structure 5. The phononic crystal layerincludes, for example, a first phononic crystal layer and a secondphononic crystal layer described later. The through holes include, forexample, first through holes and second through holes described later.In the first embodiment, all the thermoelectric conversion elements 21include the respective phononic crystal layers.

However, not all the thermoelectric conversion element 21 may includethe phononic crystal layers. The term “substantially parallel” as usedherein means that, even when the relation between two directionsdeviates from a parallel relation by, for example, 5 degrees or less,preferably 3 degrees of less, and more preferably 1 degree or less,these directions are regarded as parallel to each other.

In insulators and semiconductors, heat is transferred mainly by latticevibrations called phonons. The thermal conductivity of a materialcomposed of an insulator or a semiconductor is determined by thedispersion relation of phonons in the material. The dispersion relationof phonons means the relation between their frequency and wavenumber orthe band structure of phonons. In insulators and semiconductors, phononsthat transfer heat are present in a wide frequency band of from 100 GHzto 10 THz. This frequency band is a thermal band. The thermalconductivity of a material is determined by the dispersion relation ofphonons in the thermal band. In the phononic crystal structures, thedispersion relation of phonons in the material can be controlled by theperiodic structure formed from the through holes. In other words, in athermoelectric converter having a phononic crystal structure, thethermal conductivity itself of the material of the thermoelectricconverter such as its base material can be controlled. In particular,the formation of a phononic band gap (PBG) by the phononic crystalstructure can significantly reduce the thermal conductivity of thematerial. No phonons are allowed to be present in the PBG. Therefore,the PBG located in the thermal band can serve as a gap for thermalconduction. Moreover, in frequency bands other than the PBG, thegradients of the phonon dispersion curves are reduced by the PBG. Thereduction in the gradients reduces the group velocity of phonons,causing a reduction in the speed of heat conduction. Thesecharacteristics significantly contribute to a reduction in the thermalconductivity itself of the material.

<Phononic Crystal Structure>

A description will be given of a phononic crystal structure that thethermoelectric converter of each thermoelectric conversion element 21can have. The p-type thermoelectric converter 22 is exemplified as thethermoelectric converter. The n-type thermoelectric converter 23 canalso have the phononic crystal structure described below.

FIG. 2 shows an example of the p-type thermoelectric converter 22. Thep-type thermoelectric converter 22 in FIG. 2 includes a first phononiccrystal layer 44 having a first phononic crystal structure including aplurality of first through holes 43 arranged regularly. The p-typethermoelectric converter 22 in FIG. 2 is a monolayer structural bodyincluding the first phononic crystal layer 44. The through direction ofthe plurality of first through holes 43 in the first phononic crystalstructure and in the first phononic crystal layer 44 is a directionconnecting a first end 41 of the p-type thermoelectric converter 22 andits second end 42. The first electrode 24 is disposed on the first end41. The second electrode 25 is disposed on the second end 42. The abovedirection is substantially perpendicular to the connection surfacebetween the p-type thermoelectric converter 22 and the first electrode24 and the connection surface between the p-type thermoelectricconverter 22 and the second electrode 25. The term “substantiallyperpendicular” as used herein means that, even when the relation betweentwo directions deviates from a perpendicular relation by, for example, 5degrees or less, preferably 3 degrees or less, and more preferably 1degree or less, these directions are regarded as perpendicular to eachother.

Another example of the p-type thermoelectric converter 22 is shown inFIG. 3. The p-type thermoelectric converter 22 shown in FIG. 3 furtherincludes, in addition to the first phononic crystal layer 44, a secondphononic crystal layer 46 having a second phononic crystal structureincluding a plurality of second through holes 45 arranged regularly. Thefirst phononic crystal layer 44 and the second phononic crystal layer 46are stacked in a direction connecting the first end 41 and the secondend 42 of the p-type thermoelectric converter 22. The first phononiccrystal layer 44 and the second phononic crystal layer 46 are stacked inthe stacking direction of the layered structure 5. The through directionof the plurality of first through holes 43 in the first phononic crystalstructure and in the first phononic crystal layer 44 is substantiallyparallel to the through direction of the plurality of second throughholes 45 in the second phononic crystal structure and in the secondphononic crystal layer 46. The p-type thermoelectric converter 22 inFIG. 3 is a multilayer structural body including the first phononiccrystal layer 44 and the second phononic crystal layer 46. The firstphononic crystal layer 44 and the second phononic crystal layer 46 arein contact with each other.

The PBG is distributed three-dimensionally, and it is expected that aheat flow in each phononic crystal layer can be controlled not only inits in-plane directions but also in its thickness direction and that thethermal conductivity can be reduced by controlling the heat flow. Thephrase “the thickness direction of a phononic crystal layer” means thethrough direction of a plurality of regularly arranged through holes inFIGS. 2 and 3. In the p-type thermoelectric converter 22 in FIG. 3, atleast two phononic crystal layers are stacked in the thicknessdirection. It is expected that the stack with an increased thicknesswill allow the heat flow in the p-type thermoelectric converter 22 inthe thickness direction to be controlled more reliably.

The thickness of the first phononic crystal layer 44 and the thicknessof the second phononic crystal layer 46 are, for example, equal to ormore than 10 nm and equal to or less than 500 nm. When the p-typethermoelectric converter 22 includes two or more phononic crystallayers, the thicknesses of these phononic crystal layers may be the sameas or different from each other.

No limitation is imposed on the number of phononic crystal layersincluded in the p-type thermoelectric converter 22. When the p-typethermoelectric converter 22 includes two or more phononic crystallayers, the phononic crystal layers may be stacked in contact with eachother or may be stacked with another member interposed therebetween. Theother member is, for example, an oxide film such as a SiO₂ film or abuffer layer described later.

FIG. 4 is a plan view showing the p-type thermoelectric converter 22 inFIG. 3 when it is viewed from the first phononic crystal layer 44 side.FIG. 5 is a plan view showing the p-type thermoelectric converter 22 inFIG. 3 when it is viewed from the second phononic crystal layer 46 side.In the p-type thermoelectric converter 22 in FIGS. 3, 4, and 5, thefirst phononic crystal structure that the first phononic crystal layer44 has structurally differs from the second phononic crystal structurethat the second phononic crystal layer 46 has. Specifically, the periodP of the arrangement of the first through holes 43 differs from theperiod P of the arrangement of the second through holes 45. When thefirst phononic crystal structure structurally differs from the secondphononic crystal structure, at least part of the second through holes 45are generally not in communication with the first through holes 43. In ap-type thermoelectric converter 22 including two or more phononiccrystal layers, the phononic crystal layers may be structurally the sameas each other.

The thickness of the phononic crystal layers 44 and 46 that correspondsto the length of the through holes 43 and 45 may be equal to or largerthan twice the diameter of the through holes. In this case, the distancebetween the upper and lower surfaces of each of the phononic crystallayers 44 and 46 can be increased. This allows the temperaturedifference between the upper and lower surfaces of each of the phononiccrystal layers 44 and 46 to be increased, so that the thermoelectricconversion efficiency can be improved.

As used herein, the term “the upper surface” and “the lower surface” ofa phononic crystal layer mean, respectively, one principal surface ofthe phononic crystal layer and the other principal surface opposite tothe one principal surface when the phononic crystal layer is viewed inthe through direction of the through holes. The term “the principalsurface” means a surface having the largest area. The upper limit of thethickness of each of the phononic crystal layers 44 and 46 is, forexample, equal to or less than 100 times the diameter of the throughholes and may be equal to or less than 80 times, equal to or less than60 times, and equal to or less than 50 times the diameter of the throughholes.

The ratio of the total volume of the through holes 43 or 45 included ineach of the phononic crystal layers 44 and 46 to the volume of the eachof the phononic crystal layers 44 and 46, i.e., the porosity of thephononic crystal layer, may be equal to or more than 10%. In this case,the volumes of the phononic crystal layers 44 and 46 excluding thethrough holes 43 and 45 can be reduced, so that the effect of the PBGcan be increased. Therefore, the thermal conductivity of each of thephononic crystal layers 44 and 46 can be further reduced, and thethermoelectric conversion efficiency can be increased. The upper limitof the porosity of each of the phononic crystal layers 44 and 46 is, forexample, equal to or lower than 90% and may be equal or lower than 70%,equal to or lower than 50%, and equal to or lower than 40%.

Examples of the case where the first phononic crystal structurestructurally differs from the second phononic crystal structure includethe following cases. A plurality of cases may be used in combination.

-   -   The period P of the arrangement of the first through holes 43        differs from the period P of the arrangement of the second        through holes 45.    -   The diameter D of the first through holes 43 differs from the        diameter D of the second through holes 45.    -   The type of unit cell 91 including first through holes 43        differs from the type of unit cell 91 including second through        holes 45.

As shown in a phononic crystal structure A described later, thearrangement of the first through holes 43 in the first phononic crystalstructure and the arrangement of the second through holes 45 in thesecond phononic crystal structure are not always constant over theentire phononic crystal layers. In consideration of the above, when thefirst phononic crystal structure structurally differs from the secondphononic crystal structure, the p-type thermoelectric converter 22 canhave configurations described below. The p-type thermoelectric converter22 may have a configuration obtained by combining any of theconfigurations described below.

Configuration A: The first phononic crystal structure includes a domainA that is a phononic crystal region. The second phononic crystalstructure includes a domain B that is a phononic crystal region. Thedomain A and the domain B overlap with each other when viewed in thethrough direction of the first through holes 43 and the second throughholes 45. The period P of the arrangement of the first through holes 43in the domain A differs from the period of the arrangement of the secondthrough holes 45 in the domain B.

Configuration B: The first phononic crystal structure includes a domainA that is a phononic crystal region. The second phononic crystalstructure includes a domain B that is a phononic crystal region. Thedomain A and the domain B overlap with each other when viewed in thethrough direction of the first through holes 43 and the second throughholes 45. The diameter of the first through holes 43 in the domain Adiffers from the diameter of the second through holes 45 in the domainB.

Configuration C: The first phononic crystal structure includes a domainA that is a phononic crystal region. The second phononic crystalstructure includes a domain B that is a phononic crystal region. Thedomain A and the domain B overlap with each other when viewed in thethrough direction of first through holes 43 and the second through holes45.

The type of unit cell including first through holes 43 in the domain Adiffers from the type of unit cell including second through holes 45 inthe domain B.

Each of the domains, which are phononic crystal regions, is a regionhaving an area of, for example, equal to or more than 25 P² in planview, where P is the period of the arrangement of the through holes 43or 45. To control the dispersion relation of phonons using the phononiccrystal structure, the domain may have an area of at least equal to ormore than 25 P². When the length of the sides of a square domain in planview is equal to or more than 5>P, the area of the domain can be equalto or more than 25 P².

No limitation is imposed on the shape of each domain in plan view. Theshape of each domain in plan view is, for example, a polygonal shapesuch as a triangular, square, or rectangular shape, a circular shape, anelliptical shape, or a combination thereof. Each domain may have anirregular shape in plan view. No limitation is imposed on the number ofdomains included in each phononic crystal structure. No limitation isimposed on the size of each domain included in the phononic crystalstructure. One domain may be spread over the entire phononic crystallayer. The term “in plan view” as used herein means that the phononiccrystal layer is viewed in the through direction of the through holes.

The period P of the arrangement of the through holes 43 or 45 is, forexample, equal to or more than 1 nm and equal to or less than 300 nm.This is because the wavelength of phonons carrying heat ranges mainlyfrom 1 nm to 300 nm. The period P is determined by the center-to-centerdistance between adjacent through holes 43 or 45 in plan view.

The diameter D of the through holes 43 or 45 satisfies, for example,D/P≥0.5, where D/P is the ratio of the diameter D to the period P. Ifthe ratio D/P<0.5, the porosity of the phononic crystal structure isexcessively small, so that the heat flow may not be controlledsufficiently, e.g., the thermal conductivity may not be sufficientlyreduced. The upper limit of the ratio D/P is, for example, less than 0.9in order to prevent contact between adjacent through holes 43 or 45. Thediameter D of the through holes 43 or 45 is the diameter of theiropenings. When the openings of the through holes 43 or 45 have acircular shape in plan view, the diameter D is the diameter of thecircular shape. The openings of the through holes 43 or 45 may have anon-circular shape in plan view. In this case, the diameter D is definedas the diameter of a virtual circle having the same area as the area ofthe openings.

Examples of the type of unit cell 91 including a plurality of regularlyarranged through holes 43 or 45 include a square lattice (FIG. 6A), ahexagonal lattice (FIG. 6B), a rectangular lattice (FIG. 6C), and acentered rectangular lattice (FIG. 6D). However, the type of unit cell91 is not limited to these examples.

The material M forming the p-type thermoelectric converter 22, then-type thermoelectric converter 23, and the phononic crystal layers thatthe p-type thermoelectric converter 22 and the n-type thermoelectricconverter 23 can have is typically a semiconductor material doped withan impurity element such that the material is of an appropriatesemiconductor type such as the p or n type. The semiconductor materialis, for example, silicon (Si), Ge, SiGe, SiC, ZnSe, CdSn, ZnO, GaAs,InP, or GaN. The material M may be a material other than thesemiconductor materials, and such a material is, for example, TiN, SiN,or VO₂. However, the material M is not limited to the above examples.

Among semiconductor materials, a Si-based semiconductor materialgenerally has a relatively high thermal conductivity. Therefore, in aconventional thermoelectric conversion element including thermoelectricconverters formed of a Si-based semiconductor material, it is difficultto obtain high thermoelectric conversion efficiency. However, in thethermoelectric conversion element 21, the thermoelectric converters eachhave a phononic crystal layer. Therefore, in the thermoelectricconversion elements 21 and the thermoelectric conversion device 1including the thermoelectric conversion elements 21, high thermoelectricconversion efficiency can be obtained even when the thermoelectricconverters are formed of a Si-based semiconductor material.

The following advantages, for example, are obtained when thethermoelectric converters can be formed of a Si-based semiconductormaterial. The substrate 6 may be used as a base substrate.

-   -   The thermoelectric conversion elements and a thermoelectric        conversion device including these elements can be formed on a        base substrate formed of a Si-based semiconductor material such        as a Si wafer.    -   The thermoelectric conversion elements and the thermoelectric        conversion device can be embedded in a base substrate formed of        a Si-based semiconductor material. In this case, for example, an        integrated circuit such as a CPU or GPU can be formed on the        base substrate in which the thermoelectric conversion elements        or the thermoelectric conversion device is embedded. This means,        for example, that an electronic device such as an integrated        circuit device in which a Peltier-type cooling device is        embedded can be produced. The integrated circuit device may be a        semiconductor element including a thermoelectric conversion        device and an integrated circuit integrated together and housed        in one package.

The first phononic crystal structure and the second phononic crystalstructure may have the following configuration. Each phononic crystalstructure includes a first domain and a second domain that are phononiccrystal regions. The first domain has a plurality of through holesregularly arranged in a first direction in a cross section perpendicularto the through direction of the through holes. The second domain has aplurality of through holes regularly arranged in a second directiondifferent from the first direction in a cross section perpendicular tothe through direction of the through holes. Such a phononic crystalstructure having a plurality of domains distinguished by theirarrangement orientation is hereinafter referred to as a phononic crystalstructure A. The arrangement orientation can be determined by theorientation of the unit cell.

According to studies by the present inventors, the degree of reductionin thermal conductivity obtained by a phononic crystal structure dependson the angle between the direction of heat transfer and the orientationof the unit cell of the phononic crystal structure. This may be becausefactors relating to heat conduction such as the number of PBGs, the bandwidth of each PBG, the average group velocity of phonons depend on theabove angle. As for heat transfer, phonons flow in a direction from ahigh temperature side to a low temperature side in a macroscopic sense.When attention is focused on micro-regions of the order of nanometers,the flow of phonons has no directivity. Specifically, phonons do notflow in a uniform direction in a microscopic sense.

The above-described Patent Literature and Non Patent Literature disclosemembers each having a plurality of phononic crystal regions with thesame unit cell orientation. In these members, their interaction withphonons flowing in a specific direction is maximized in a microscopicsense, but the interaction with phonons flowing in the other directionsis weakened. The phononic crystal structure A includes two or morephononic crystal regions with different unit cell directions. Therefore,the interaction with phonons flowing in a plurality of directions can beenhanced in a microscopic sense. This feature allows the degree offlexibility in controlling the heat flow to be further improved.

The following description relates to the phononic crystal structure Athat at least one phononic crystal layer selected from the firstphononic crystal layer 44 and the second phononic crystal layer 46 canhave. When a plurality of phononic crystal layers have their respectivephononic crystal structures A, these phononic crystal structures A maybe structurally the same as or different from each other.

An example of the phononic crystal structure A is shown in FIG. 7. FIG.7 shows a plan view of part of a phononic crystal layer 56. The phononiccrystal layer 56 may be at least one phononic crystal layer selectedfrom the first phononic crystal layer 44 and the second phononic crystallayer 46. The phononic crystal layer 56 is a thin film having athickness of, for example, equal to or larger than 10 nm and equal to orless than 500 nm. The phononic crystal layer 56 is rectangular in planview. A plurality of through holes 50 extending in the thicknessdirection of the phononic crystal layer 56 are provided in the phononiccrystal layer 56. The phononic crystal structure A that the phononiccrystal layer 56 has is a two-dimensional phononic crystal structure inwhich the plurality of through holes 50 are regularly arranged inin-plane directions.

The phononic crystal structure A includes the first domain 51A and thesecond domain 51B that are phononic crystal regions. The first domain51A has a phononic single crystal structure including a plurality ofthrough holes 50 arranged regularly in a first direction in plan view.The second domain 51B has a phononic single crystal structure includinga plurality of through holes 50 arranged regularly in a second directiondifferent from the first direction in plan view. In each of the singlecrystal structures, the plurality of through holes 50 have the samediameter and arranged with the same period. In each of the singlecrystal structures, the orientations of unit cells 91A or 91B of theplurality of regularly arranged through holes 50 are the same as eachother. The first domain 51A and the second domain 51B each have arectangular shape in plan view. The shape of the first domain 51A andthe shape of the second domain 51B are the same in plan view. Thephononic crystal structure A is also a phononic polycrystal structure 52that is a complex body including a plurality of phononic single crystalstructures.

As shown in FIGS. 8A and 8B, in the phononic crystal structure A, theorientation 53A of each unit cell 91A in the first domain 51A differsfrom the orientation 53B of each unit cell 91B in the second domain 51Bin plan view. The angle between the orientation 53A and the orientation53B in plan view is, for example, equal to or more than 10 degrees. Whenthe unit cell 91A and the unit cell 91B are identical and have an n-foldrotational symmetry, the upper limit of the angle between theorientation 53A and the orientation 53B is less than 360/n degrees. Wheneach unit cell has n-fold symmetries for a plurality of n's, the largestone of the n's is used to determine the upper limit of the angle. Forexample, a hexagonal lattice has a 2-fold rotational symmetry, a 3-foldrotational symmetry, and a 6-fold rotational symmetry. In this case, “6”is used for the n defining the upper limit of the angle. Specifically,when the unit cells 91A and 91B are each a hexagonal lattice, the anglebetween the orientation 53A and the orientation 53B is less than 60degrees. The phononic crystal structure A includes at least two phononiccrystal regions having different unit cell orientations. The phononiccrystal structure A may further include any other phononic crystalregions and/or regions having no phononic crystal structure so long asthe above condition is met.

The orientation of a unit cell can be determined based on any rule.However, it is necessary that the same rule be applied to differentdomains to determine the orientations of their unit cells. Theorientation of a unit cell is, for example, the extending direction of astraight line bisecting the angle between two non-parallel sidesincluded in the unit cell. However, it is necessary to use the same rulefor different domains to define their two sides.

FIG. 9 shows an enlarged view of region R1 in the phononic crystalstructure A in FIG. 7. The orientations 53A and 53B of the unit cells91A and 91B change at the interface 55 between the first domain 51A andthe second domain 51B adjacent to each other. The interface 55 at whichthe orientations of the unit cells change has a large interfaceresistance to heat macroscopically flowing through the phononic crystalstructure A. The interface resistance is based on a mismatch between thegroup velocity of phonons in the first domain 51A and the group velocityof phonons in the second domain 51B. The interface resistancecontributes to a reduction in the thermal conductivity of the phononiccrystal layer 56 having the phononic crystal structure A. In FIG. 9, theinterface 55 extends linearly in plan view. The interface 55 extends inthe width direction of the rectangular phononic crystal layer 56 in planview. The width direction may be a direction perpendicular to theextending direction of the centerline of the phononic crystal layer 56that is determined by the direction of macroscopic heat transfer. Theinterface 55 divides the phononic crystal structure A in a directionsubstantially perpendicular to the direction of macroscopic heattransfer in plan view.

In the phononic crystal structure A in FIG. 7, the period P of thearrangement of the plurality of through holes 50 in the first domain 51Ais the same as the period P of the arrangement of the plurality ofthrough holes 50 in the second domain 51B.

In the phononic crystal structure A in FIG. 7, the diameter of theplurality of through holes 50 regularly arranged in the first domain 51Ais the same as the diameter of the plurality of through holes 50regularly arranged in the second domain 51B.

In the phononic crystal structure A in FIG. 7, the type of unit cell 91Ain the first domain 51A is the same as the type of unit cell 91B in thesecond domain 51B. The unit cell 91A and the unit cell 91B in FIG. 7 areeach a hexagonal lattice.

No limitation is imposed on the number of domains included in thephononic crystal structure A. The larger the number of domains includedin the phononic crystal structure A is, the larger the effect of theinterface resistance at the interfaces between domains is.

Other examples of the phononic crystal structure A will be shown.

In a polycrystal structure 52 that is a phononic crystal structure A inFIGS. 10 and 11, the interface 55 between a first domain 51A and asecond domain 51B adjacent to each other extends in the direction of thelong sides of the rectangular phononic crystal layer 56 in plan view.The phononic crystal structure A in FIGS. 10 and 11 is structurally thesame as the phononic crystal structure A in FIG. 7 except for the abovefeature. FIG. 11 is an enlarged view of region R2 in FIG. 10.

In the phononic crystal structures A in FIGS. 7 and 10, the size of thefirst domain 51A is the same as the size of the second domain 51B inplan view. However, the sizes of the first and second domains 51A and51B included in a phononic structure A may differ from each other inplan view.

In a polycrystal structure 52 that is a phononic crystal structure A inFIGS. 12 and 13, a first domain 51B is surrounded by a second domain 51Ain plan view. The first domain 51A has a rectangular outer shape in planview. The second domain 51B has a rectangular shape in plan view. Thesize of the first domain 51A differs from the size of the second domain51B in plan view. In plan view, the interface 55 between the seconddomain 51B and the first domain 51A surrounding the second domain 51Bforms the outer edge of the second domain 51B. The phononic crystalstructure A in FIGS. 12 and 13 is structurally the same as the phononiccrystal structure A in FIG. 7 except for the above feature. FIG. 13 isan enlarged view of region R3 in FIG. 12.

In the phononic crystal structure A in FIGS. 12 and 13, the interface 55has bent portions.

Moreover, the phononic crystal structure A in FIGS. 12 and 13 includesthe second domain 51B that is not in contact with the sides of thephononic crystal layer 56.

In a polycrystal structure 52 that is a phononic crystal structure A inFIG. 14, a first domain 51A and a second domain 51B are disposed so asto be spaced apart from each other in plan view. More specifically, inplan view, a region 201 having no through holes 50 is disposed betweenthe first domain 51A and the second domain 51B so as to extend in thelong side direction of the phononic crystal layer 56. The phononiccrystal structure A in FIG. 14 is structurally the same as the phononiccrystal structure A in FIG. 7 except for the above feature.

In a polycrystal structure 52 that is a phononic crystal structure A inFIG. 15, a first domain 51A and a second domain 51B are disposed so asto be spaced apart from each other in plan view. More specifically, inplan view, a region 202 having randomly arranged through holes 50 isdisposed between the first domain 51A and the second domain 51B so as toextend in the long side direction of the phononic crystal layer 56. Inthe region 202, the through holes 50 are not arranged regularly in planview. Alternatively, in the region 202, the area of a regulararrangement region is, for example, less than 25 P² in plan view. Here,P is the period of the arrangement of the through holes 50. The phononiccrystal structure A in FIG. 15 is structurally the same as the phononiccrystal structure A in FIG. 7 except for the above feature.

A polycrystal structure 52 that is a phononic crystal structure A inFIG. 16 includes a plurality of domains 51A, 51B, 51C, 51D, 51E, 51F,and 51G having different shapes in plan view. In each of the domains,the period of the arrangement of a plurality of through holes 50 and theunit cell orientation are constant. However, the unit cell orientationsof the domains differ from each other. In plan view, the sizes andshapes of the domains differ from each other. In this configuration, thenumber of unit cell orientations in the phononic crystal structure A asa whole is larger than that in the configurations exemplified above.Therefore, the effect of reducing the thermal conductivity that is basedon the difference in unit cell orientation is more significant. In thisconfiguration, interfaces 55 between the domains extend in a pluralityof random directions in plan view. Therefore, the effect of reducing thethermal conductivity based on the interface resistance is moresignificant.

In the phononic crystal structure A in FIG. 16, the interface 55 betweenthe first domain 51A and the second domain 51B adjacent to each otherextends in a direction inclined with respect to the width direction ofthe phononic crystal layer 56 in plan view. The interfaces 55 also havebent portions in plan view.

A polycrystal structure 52 that is a phononic crystal structure A mayinclude a first domain 51A and a second domain 51B that differ in theperiod P of the arrangement of through holes 50 and/or in the diameter Dof the through holes 50. The diameter D of through holes 50 in a firstdomain 51A shown in FIG. 17A differs from the diameter D of throughholes 50 in a second domain 51B shown in FIG. 17B. The period P of thearrangement of the through holes 50 in the first domain 51A shown inFIG. 17A is the same as the period P of the arrangement of the throughholes 50 in the second domain 51B shown in FIG. 17B.

A phononic crystal structure A shown in FIG. 18 has a first domain 51Ain which a plurality of through holes 50 having a smaller diameter D areregularly arranged with a smaller period P and a second domain 51B inwhich a plurality of through holes 50 having a larger diameter D areregularly arranged with a larger period P. The phononic crystalstructure A shown in FIG. 18 includes a region 92 including a pluralityof through holes 50 with a smaller period P and a smaller diameter D anda region 93 including a plurality of through holes 50 with a largerperiod P and a larger diameter D. The region 92 is adjacent to theregion 93. The region 92 and the region 93 each include a plurality ofdomains having different shapes and different unit cell orientations inplan view, as in the example shown in FIG. 16. The region 92 and theregion 93 divide the phononic crystal structure A in a directionsubstantially parallel to the direction of macroscopic heat transfer. Inthis configuration, the frequency band of a PBG formed in the firstdomain 51A differs from the frequency band of a PBG formed in the seconddomain 51B, and therefore, the effect of reducing the thermalconductivity is particularly significant.

A phononic crystal structure A shown in FIG. 19 includes a first domain51A in which a plurality of through holes 50 having a smaller diameter Dare regularly arranged with a smaller period P and a second domain 51Bin which a plurality of through holes 50 having a larger diameter D areregularly arranged with a larger period P. The phononic crystalstructure A in FIG. 19 includes a plurality of domains having differentshapes in plan view and different unit cell orientations. In thisconfiguration, the frequency band of a PBG formed in the first domain51A differs from the frequency band of a PBG formed in the second domain51B, and therefore the effect of reducing the thermal conductivity isparticularly significant.

The phononic crystal layer 56 has, for example, a polygonal shape suchas a triangular, square, or rectangular shape, a circular shape, anelliptical shape, or a combination thereof in plan view. However, theshape of the phononic crystal layer 56 is not limited to the aboveexamples.

The thermoelectric converter has, for example, a polygonal shape such asa triangular, square, or rectangular shape, a circular shape, anelliptical shape, or a combination thereof in plan view. However, theshape of the thermoelectric converter is not limited to the aboveexamples. The thermoelectric converter may have a rectangularparallelepipedic or cubic shape.

The thermoelectric converter may include two or more first phononiccrystal layers 44 and/or two or more second phononic crystal layers 46.The thermoelectric converter may further include a phononic crystallayer having a phononic crystal structure having a configurationdifferent from those of the first phononic crystal structure and thesecond phononic crystal structure.

Another example of the phononic crystal layer 56 is shown in FIGS. 20Aand 20B. FIG. 20B shows a cross section 20B-20B of the phononic crystallayer 56 in FIG. 20A. The phononic crystal layer 56 shown in FIGS. 20Aand 20B further includes a plurality of pillars 61. The pillars 61 arecolumnar members extending linearly. Each of the pillars 61 is filledinto a corresponding one of the through holes 50 in the phononic crystallayer 56. The circumferential surface of each of the pillars 61 iscovered with an oxide film 62. In this configuration, the through holes50 that are vacant holes are filled with the respective pillars 61.Therefore, for example, the degree of flexibility in controlling thecharacteristics of the phononic crystal layer 56 in the throughdirection of the through holes 50 can be increased. More specifically,for example, in a thermoelectric converter that is a stacked structuralbody including two or more phononic crystal layers 56, the electronconductivity between a first end 41 and a second end 42 can be improvedwhile the low thermal conductivity based on the phononic crystalstructures is maintained.

When the material the phononic crystal layer 56 into which the pillars61 have been filled is the same as the material of the pillars 61, thecircumferential surface of each of the pillars 61 is covered with theoxide film 62. When the material the phononic crystal layer 56 intowhich the pillars 61 have been filled is different from the material ofthe pillars 61, the oxide film 62 is not always necessary.

The phononic crystal layer 56 further including the pillars 61 is, forexample, the first phononic crystal layer 44 and/or the second phononiccrystal layer 46. The pillars 61 may be filled into the first throughholes 43 and also into the second through holes 45.

Typically, the pillars 61 are formed of a semiconductor material. Thematerial forming the pillars 61 is, for example, Si, SiGe, SiC, TiN,SiN, or VO₂. However, the material forming the pillars 61 is not limitedto the above examples.

The oxide film 62 is, for example, a SiO₂ film. However, the oxide film62 is not limited to the above example.

FIG. 21 shows an example of the p-type thermoelectric converter 22including the first phononic crystal layer 44 and the second phononiccrystal layer 46 with the pillars 61 filled thereinto. The p-typethermoelectric converter 22 in FIG. 21 includes the phononic crystallayers 56 shown in FIGS. 20A and 20B as the first phononic crystal layer44 and the second phononic crystal layer 46. The p-type thermoelectricconverter 22 in FIG. 21 is a two-layer structural body including twophononic crystal layers 56. A buffer layer 63 is disposed between thefirst phononic crystal layer 44 and the second phononic crystal layer46. The material forming the pillars 61 (excluding the oxide film 62) inthe first phononic crystal layer 44 is the same as the material formingthe buffer layer 63. The material forming the buffer layer 63 is thesame as the material forming the second phononic crystal layer 46(excluding the pillars 61 and the oxide film 62).

Another example of the phononic crystal layer 56 is shown in FIGS. 22Aand 22B. FIG. 22B shows a cross section 22B-22B of the phononic crystallayer 56 in FIG. 22A. The phononic crystal layer 56 shown in FIGS. 22Aand 22B further includes a plurality of pillars 61. Each of the pillars61 is filled into a corresponding one of the through holes 50 in thephononic crystal layer 56. The material forming the pillars 61 differsfrom the material forming the phononic crystal layer 56.

FIG. 23 shows an example of the p-type thermoelectric converter 22including the first phononic crystal layer 44 and the second phononiccrystal layer 46 with pillars 61 filled thereinto. The p-typethermoelectric converter 22 in FIG. 23 is a three-layer structural bodywhich includes three phononic crystal layers 56 and in which a firstphononic crystal layer 44, a second phononic crystal layer 46, and afirst phononic crystal layer 44 are disposed in this order. A firstbuffer layer 63A is disposed between the lowermost first phononiccrystal layer 44 and the second phononic crystal layer 46. A secondbuffer layer 63B is disposed between the second phononic crystal layer46 and the uppermost first phononic crystal layer 44. The materialforming the pillars 61 in the first phononic crystal layer 44 is thesame as the material forming the second buffer layer 63B.

The material forming the pillars 61 in the second phononic crystal layer46 is the same as the material forming the first buffer layer 63A. Thematerial forming the first phononic crystal layers 44 (excluding thepillars 61) is the same as the material forming the first buffer layer63A. The material forming the second phononic crystal layer 46(excluding the pillars 61) is the same as the material forming thesecond buffer layer 63B. The p-type thermoelectric converter 22 in FIG.23 is formed from two types of materials. The two types of materials maybe semiconductor materials.

The first connection electrode 11, the second connection electrode 12,the third connection electrode 13, the fourth connection electrode 14,the first electrodes 24, the second electrodes 25, and the thirdelectrodes 26 are each formed of a conductive material. The conductivematerial is typically a metal. The metal is, for example, chromium (Cr),aluminum (Al), gold (Au), silver (Ag), or copper (Cu). However, theconductive material is not limited to the above examples. At least oneselected from the first connection electrode 11, the second connectionelectrode 12, the third connection electrode 13, the fourth connectionelectrode 14, the first electrodes 24, the second electrodes 25, and thethird electrodes 26 may include a phononic crystal layer. The throughdirection of the plurality of through holes in the phononic crystallayer may be substantially parallel to the stacking direction of thelayered structure 5.

The substrate (base layer) 6 is typically formed of a semiconductormaterial. The semiconductor material is, for example, Si. The substrate6 may be a Si wafer. An oxide film may be formed on the upper surface ofthe substrate 6 formed of Si. The oxide film is, for example, a SiO₂film. The oxide film may be the second insulating layer 7. The structureof the substrate 6 is not limited to the above example. For example, anintegrated circuit may be embedded in the substrate 6. The substrate 6may have a multilayer structure including a plurality of stacked layers.At least part of the substrate 6 may include a phononic crystal layer.The through direction of the plurality of through holes in the phononiccrystal layer may be substantially parallel to the stacking direction ofthe layered structure 5.

The first insulating layer 3 may function as a layer for maintainingelectrical insulation between the first thermoelectric conversion module2 and the second thermoelectric conversion module 4. The secondinsulating layer 7 may function as a layer for maintaining electricalinsulation between the substrate 6 and the first thermoelectricconversion module 2. The first insulating layer 3, the second insulatinglayer 7, and the insulating portions 27 are typically formed of aninsulating material. The insulating material is, for example, any ofoxides, nitrides, and oxynitrides of metals including Si. The insulatingmaterial may be SiO₂. However, the insulating material is not limited tothe above examples. At least one selected from the first insulatinglayer 3, the second insulating layer 7, and the insulating portions 27may include a phononic crystal layer. The through direction of theplurality of through holes in the phononic crystal layer may besubstantially parallel to the stacking direction of the layeredstructure 5.

The protective layer 8 may function as a layer that protects thethermoelectric conversion device 1. The protective layer 8 is formed of,for example, an insulating material. Examples of the insulating materialare as described above. The protective layer 8 may include a phononiccrystal layer. The through direction of the plurality of through holesin the phononic crystal layer may be substantially parallel to thestacking direction of the layered structure 5.

When a member of each thermoelectric conversion element 21 other thanthe thermoelectric converters includes a phononic crystal layer, thethermal conductivity of the thermoelectric conversion device 1 inin-plane directions can be reduced. This reduction allows thethermoelectric conversion efficiency of the thermoelectric conversiondevice 1 to be further improved. Moreover, the reduction can inhibit thediffusion of heat in the in-plane directions, so that the degree offlexibility in the construction of an electronic device including thethermoelectric conversion device 1 can be increased.

The thermoelectric conversion device 1 may further include a temperaturedetection module. In this case, for example, the first thermoelectricconversion module 2 and/or the second thermoelectric conversion module 4can be controlled based on the information about temperature acquired bythe temperature detection module. The information about the temperatureis, for example, the value of the temperature, the rate of change in thetemperature, or the history of the temperature. However, the informationabout the temperature is not limited to the above examples. Thethermoelectric conversion device 1 in FIG. 1 includes a temperaturedetection module 28 disposed inside the first insulating layer 3. Thetemperature detection module 28 is located at the center of the layeredstructure 5 when it is viewed in the stacking direction. However, thelocation of the temperature detection module 28 is not limited to theabove example. The temperature detection module 28 includes, forexample, at least one selected from a thermocouple element, a resistancethermometer bulb, and a thermistor.

The thermoelectric conversion device 1 may further include a controlmodule for controlling the voltage applied to the first thermoelectricconversion module 2 and/or the second thermoelectric conversion module4. The control module may be composed of, for example, an integratedcircuit. The control module may include a power source that applies thevoltage to the first thermoelectric conversion module 2 and/or thesecond thermoelectric conversion module 4 or may include a signaltransmitter that transmits a control signal to a power source disposedseparately from the control module. The control module may be connectedto the temperature detection module 28.

The thermoelectric conversion device 1 may further include, for example,an optional member and/or an optional module other than the componentsdescribed above.

The thermoelectric conversion device 1 can be used as a Peltier-typecooling and/or heating device. An object to be heated and/or cooled bythe thermoelectric conversion device 1 is, for example, a heat source.The heat source is, for example, an integrated circuit such as a CPU ora GPU or an integrated circuit device including the integrated circuit.However, the object is not limited to the above examples. The amount ofheat generated by an integrated circuit varies irregularly depending onthe load thereon.

Therefore, although it is desirable that the temperature of theintegrated circuit is constant, it is inevitable that the temperature ofthe integrated circuit varies irregularly. With the thermoelectricconversion device 1, for example, the irregular variations describedabove can be reduced, and the variations in the temperature of theintegrated circuit are maintained within a prescribed range. In otherwords, the thermoelectric conversion device 1 is particularlyadvantageous when the object is an integrated circuit and/or anintegrated circuit device.

The thermoelectric conversion device 1 may be used as a Seebeck-typepower generator.

<Production Method>

The thermoelectric conversion device of the present disclosure can beproduced using a combination of any of various thin film forming methodssuch as chemical vapor deposition (CVD), sputtering, and vapordeposition and any of various micromachining methods and pattern formingmethods such as electron beam lithography, photolithography, blockcopolymer lithography, selective etching, and chemo-mechanical polishing(CMP). The block copolymer lithography is suitable for the formation ofthe phononic crystal structures.

An example of a method for producing a thermoelectric conversion element21 including a phononic crystal layer will be described with referenceto FIGS. 24A to 24O. However, the method for producing thethermoelectric conversion element that the thermoelectric conversiondevice 1 can include is not limited to the following example.

FIG. 24A: A substrate 71 is prepared. An oxide film 72 has been providedon the upper surface of the substrate 71. The oxide film 72 is, forexample, a SiO₂ film.

FIG. 24B: A metal layer 73 is formed on the oxide film 72. The metallayer 73 later becomes the first electrode 24. The metal layer 73 is,for example, a Cr layer. The metal layer 73 is formed, for example, bysputtering. The thickness of the metal layer 73 is, for example, 50 nm.

FIG. 24C: A semiconductor layer 74 is formed on the metal layer 73. Thesemiconductor layer 74 is, for example, a polycrystalline Si layer. Thesemiconductor layer 74 is formed, for example, by CVD. The thickness ofthe semiconductor layer 74 is, for example, 200 nm.

FIG. 24D: A hard mask 75 is formed on the semiconductor layer 74. Thehard mask 75 is, for example, a SiO₂ layer. The hard mask 75 is formed,for example, by CVD. The thickness of the hard mask 75 is, for example,30 nm. The hard mask 75 is used to form a phononic crystal structure inthe semiconductor layer 74.

FIG. 24E: A self-assembled film 76 of a block copolymer is formed on thehard mask 75. The self-assembled film 76 is used for block copolymerlithography for forming a phononic crystal structure.

FIG. 24F: A plurality of regularly arranged through holes 77 are formedin the hard mask 75 by block copolymer lithography.

FIG. 24G: A plurality of regularly arranged through holes 50 are formedin the semiconductor layer 74 by selective etching using the hard mask75 as a resist at positions corresponding to the plurality of throughholes 77 in plan view. The plurality of through holes 50 form a phononiccrystal structure. The semiconductor layer 74 later becomes the phononiccrystal layer 56.

FIG. 24H: The hard mask 75 and the self-assembled film 76 are removed.

FIG. 24I: An oxide film 62 is formed on the inner circumferentialsurface of each of the through holes 50 in the phononic crystal layer56. The oxide film 62 is, for example, a SiO₂ film. The oxide film 62 isformed, for example, by thermal oxidation. The thickness of the oxidefilm 62 is, for example, 1 nm.

FIG. 24J: The through holes 50 in the phononic crystal layer 56 arefilled with a semiconductor to form pillars 61 having the oxide film 62on their circumferential surface. The pillars 61 are formed of, forexample, polycrystalline Si. The pillars 61 are formed, for example, byCVD. In this case, a layer 78 formed of the semiconductor materialforming the pillars 61 is formed on the phononic crystal layer 56.

FIG. 24K: The layer 78 is removed by a method such as CMP. In thismanner, the phononic crystal layer 56 further including the pillars 61is formed.

FIG. 24L: Impurity ions are implanted into a partial region of thephononic crystal layer 56 using a method such as photolithography todope the partial region with the impurity ions, and a p-typethermoelectric converter 22 is thereby formed. The impurity ions are,for example, boron ions.

FIG. 24M: Impurity ions are implanted into a region of the phononiccrystal layer 56 that differs from the p-type thermoelectric converter22 using a method such as photolithography to dope the region with theimpurity ions, and an n-type thermoelectric converter 23 is therebyformed. The impurity ions are, for example, phosphorus ions. The p-typethermoelectric converter 22 is spaced apart from the n-typethermoelectric converter 23.

FIG. 24N: The entire product is subjected to heat treatment (annealing)to activate the dopant impurity ions.

FIG. 24O: A second electrode 25 is formed on the p-type thermoelectricconverter 22. A third electrode 26 is formed on the n-typethermoelectric converter 23. The second electrode 25 and the thirdelectrode 26 are formed of, for example, Al. A thermoelectric conversionelement 21 is thereby formed. A region of the phononic crystal layer 56that remains present between the p-type thermoelectric converter 22 andthe n-type thermoelectric converter 23 serves as an insulating portion27. The insulating portion 27 has a phononic crystal structure includinga plurality of regularly arranged through holes 50. In thisconfiguration, the in-plane thermal conductivity of a portion of theelement 21 that is located between the p-type thermoelectric converter22 and the n-type thermoelectric converter 23 can be reduced. Thereduction in the in-plane thermal conductivity allows the thermoelectricconversion efficiency of the thermoelectric conversion element 21 andthe thermoelectric conversion device 1 to be further improved.

SECOND EMBODIMENT

A thermoelectric conversion device in the second embodiment is shown inFIG. 25. The thermoelectric conversion device 1 in the second embodimenthas the same structure as that of the thermoelectric conversion device 1in the first embodiment except that the thermoelectric conversion device1 further includes a third insulating layer 10 disposed on the secondthermoelectric conversion module 4 and a third thermoelectric conversionmodule 9 disposed on the third insulating layer 10 and that theprotective layer 8 is located on the third thermoelectric conversionmodule 9. The thermoelectric conversion device 1 in the secondembodiment has a structure including three thermoelectric conversionmodules 2, 4, and 9 stacked together. The thermoelectric conversiondevice of the present disclosure may include an additionalthermoelectric conversion module in addition to the first thermoelectricconversion module 2 and the second thermoelectric conversion module 4 solong as the thermoelectric conversion device has a layered structure 5.No limitation is imposed on the number of thermoelectric conversionmodules included in the thermoelectric conversion device of the presentdisclosure.

The third thermoelectric conversion module 9 includes two or morethermoelectric conversion elements 21(21 c), a fifth connectionelectrode 15, and a sixth connection electrode 16. In the thirdthermoelectric conversion module 9, the thermoelectric conversionelements 21 c are electrically connected to the fifth connectionelectrode 15 and the sixth connection electrode 16. Each thermoelectricconversion element 21 c is located on an electric path connecting theconnection electrodes 15 and 16 included in the third thermoelectricconversion module 9. By applying a voltage through the connectionelectrodes 15 and 16, the thermoelectric conversion elements 21 c andthe third thermoelectric conversion module 9 operate as Peltier elementsand Peltier modules, respectively. The third thermoelectric conversionmodule 9 may have the same structure as the structure of the firstthermoelectric conversion module 2 and/or the second thermoelectricconversion module 4 except for the features described above. In thethermoelectric conversion device 1 in the second embodiment, thethermoelectric conversion modules 2, 4, and 9 can be controlledindependently. By increasing the number of thermoelectric conversionmodules that can be controlled independently, the degree of flexibilityin controlling the cooling and/or heating of the object can be furtherimproved.

In the thermoelectric conversion device 1 in the second embodiment, alayered body including the first thermoelectric conversion module 2 andthe second thermoelectric conversion module 4 with the first insulatinglayer 3 interposed therebetween may be interpreted as a layeredstructure 5(5 a), and a layered body including the second thermoelectricconversion module 4 and the third thermoelectric conversion module 9with the third insulating layer 10 interposed therebetween may beinterpreted as a layered structure 5(5 b). The thermoelectric conversionmodules in the layered structure 5 b can be controlled independently inthe same manner as those of the layered structure 5 a. The control ofthe layered structure 5 b may be the same as the control of the layeredstructure 5 a.

THIRD EMBODIMENT

A thermoelectric conversion device in a third embodiment is shown inFIG. 26. Each of the thermoelectric conversion elements 21 in the firstembodiment and the second embodiment includes a p-type thermoelectricconverter 22 and an n-type thermoelectric converter 23 and is referredto as a 7 c-type element by those skilled in the art. The thermoelectricconversion element that the thermoelectric conversion device of thepresent disclosure can have is not limited to the 7 c-type element. Thethermoelectric conversion device 1 in the third embodiment includesthermoelectric conversion elements 31 different from the 7 c-typeelements. The thermoelectric conversion device 1 in the third embodimenthas the same structure as that of the thermoelectric conversion device 1in the first embodiment except that the thermoelectric conversionelements 31 are provided instead of the thermoelectric conversionelements 21.

Each of the thermoelectric conversion elements 31 includes twothermoelectric converters 32 and 33 adjacent to each other. Thethermoelectric converters 32 and 33 have the same conductivity type. Inother words, each thermoelectric conversion element 31 has two p-type orn-type thermoelectric converters adjacent to each other. Eachthermoelectric conversion element 31 includes a fourth electrode 34, afifth electrode 35, and a sixth electrode 36. A first end of thethermoelectric converter 32 and a first end of the thermoelectricconverter 33 are electrically connected to each other through the fourthelectrode 34. The fourth electrode 34 electrically connects the lowersurface of the thermoelectric converter 32 to the upper surface of thethermoelectric converter 33. The fourth electrode 34 includes a via line37(37 a) extending in the stacking direction of the layered structure 5.A second end of the thermoelectric converter 32 is electricallyconnected to the fifth electrode 35. A second end of the thermoelectricconverter 33 is electrically connected to the sixth electrode 36. Oneselected from the fifth electrode 35 and the sixth electrode 36 isdisposed on an electric path connecting the corresponding connectionelectrodes and located on the upstream side in the path. The otherselected from the fifth electrode 35 and the sixth electrode 36 isdisposed on the electric path connecting the corresponding connectionelectrodes and located on the downstream side in the path. In otherwords, a voltage can be applied to the thermoelectric conversion element31 through the fifth electrode 35 and the sixth electrode 36. In thethermoelectric conversion element 31, a direction connecting a pair ofelectrodes holding one of the thermoelectric converters therebetween isgenerally the stacking direction of the layered structure 5. When anelectric current is caused to flow through the electric path, thedirections of the electric current flowing through the two adjacentthermoelectric converters 32 and 33 are the same (see arrows in FIG.26). The thermoelectric conversion element 31 is known as a uni-leg typeelement to those skilled in the art.

Each of the thermoelectric conversion modules 2 and 4 in FIG. 26includes two or more thermoelectric conversion elements 31. In twoelements 31 adjacent to each other, the fifth electrode 35 of oneelement 31 and the sixth electrode 36 of the other element 31 areelectrically connected through a via line 37(37 b) extending in thestacking direction of the layered structure 5.

Each thermoelectric conversion element 31 can have any known uni-legtype structure so long as the thermoelectric converters each have aphononic crystal layer.

[Method for Controlling Thermoelectric Conversion Device]

An example of a method for controlling the thermoelectric conversiondevice 1 is shown in FIG. 27. The control method in FIG. 27 includes astep of applying a first voltage to a first thermoelectric conversionmodule 2 and applying a second voltage to a second thermoelectricconversion module 4. The application pattern of the first voltagediffers from the application pattern of the second voltage. The controlmethod in FIG. 27 is a method for independently controlling thethermoelectric conversion modules included in the thermoelectricconversion device 1.

Examples of the form of the application pattern are as follows. However,the form of the application pattern is not limited to the followingexamples.

-   -   At least one selected from the effective voltage value, the        maximum voltage value, and the minimum voltage value is        different.    -   At least one selected from the width of pulses, their period,        their waveform, and the duty cycle during the application of the        pulses is different.

When the thermoelectric conversion device includes the first temperaturedetection module 28, the application pattern of the first voltage and/orthe application pattern of the second voltage may be controlled based onthe information about the temperature acquired by the temperaturedetection module 28.

The object to be cooled and/or heated by the thermoelectric conversiondevice 1 may be disposed near the thermoelectric conversion device 1.The object is, for example, a heat source. Examples of the heat sourceare as described above. The object is disposed, for example, at aposition opposite to the substrate 6 of the thermoelectric conversiondevice 1. The object may be in contact with the thermoelectricconversion device 1. The object may be in contact with the protectivelayer 8, the insulating layer, or one of the thermoelectric conversionmodules of the thermoelectric conversion device 1. In this case, atleast one selected from the following control A, control B, and controlC may be performed.

Control A: The object includes a second temperature detection module, orthe second temperature detection module is disposed between the objectand the thermoelectric conversion device 1. Based on the informationabout temperature acquired by the second temperature detection module,the application pattern of the first voltage and/or the applicationpattern of the second voltage is controlled. In this manner, the degreeof flexibility in controlling the cooling and/or heating of the objectcan be further improved.

Control B: The application pattern of the first voltage and/or theapplication pattern of the second voltage is controlled such that thevoltage applied to a thermoelectric conversion module that is selectedfrom a group of thermoelectric conversion modules included in thethermoelectric conversion device 1 and is closer to the object ischanged more frequently than the voltage applied to a thermoelectricconversion module farther from the object. The group of thermoelectricconversion modules in each of first and third embodiments 1 and 3includes the first thermoelectric conversion module 2 and the secondthermoelectric conversion module 4. The group of thermoelectricconversion modules in the second embodiment includes the firstthermoelectric conversion module 2, the second thermoelectric conversionmodule 4, and the third thermoelectric conversion module 9.

Among a thermoelectric conversion module group including three or morethermoelectric conversion modules, any two thermoelectric conversionmodules adjacent to each other with an insulating layer interposedtherebetween may be selected as the first thermoelectric conversionmodule 2 and the second thermoelectric conversion module 4 to which thefirst voltage and the second voltage, respectively, are to be applied.

Control C: The application pattern of the first voltage and/or theapplication pattern of the second voltage is controlled such thatvariations in the temperature of the object are within a prescribedrange.

A more specific example of the control B is shown in FIGS. 28 and 29. Acontrol method in FIGS. 28 and 29 is a method for controlling athermoelectric conversion device 1 including three thermoelectricconversion modules. In the control method in FIGS. 28 and 29, thevoltage application patterns are controlled such that the voltageapplied to a thermoelectric conversion module A closest to the object ischanged more frequently than the voltages applied to thermoelectricconversion modules B and C farther from the object. Moreover, thevoltage application patterns are controlled such that the voltageapplied to the thermoelectric conversion module B is changed morefrequently than the voltage applied to the thermoelectric conversionmodule C farther from the object than the thermoelectric conversionmodule B. In the control in FIG. 29, voltages are applied irregularly tothe thermoelectric conversion modules A and B.

The above control method is also a method for cooling and/or heating theobject using the thermoelectric conversion device 1. In other words, inanother aspect different from the above aspect, the present disclosureprovides a method for cooling and/or heating an object using athermoelectric conversion device. In this method, the thermoelectricconversion device is the thermoelectric conversion device of the presentdisclosure. The method includes a step of applying a first voltage to afirst thermoelectric conversion module of the thermoelectric conversiondevice and applying a second voltage to a second thermoelectricconversion module in an application pattern different from that for thefirst voltage. In this method, one or two or more types of controldescribed above can be performed.

Electronic Device]

In another aspect, the present disclosure provides an electronic deviceincluding an integrated circuit and a thermoelectric conversion devicethat cools and/or heats the integrated circuit. The thermoelectricconversion device is the thermoelectric conversion device of the presentdisclosure. Examples of the electronic device are as described above.

INDUSTRIAL APPLICABILITY

The thermoelectric conversion device of the present disclosure can beused as, for example, a Peltier-type cooling device and/or aPeltier-type heating device.

Examples of the invention derived from the above-disclosed contents areenumerated below.

(Item 1)

A thermoelectric conversion device including:

-   -   a first thermoelectric conversion module;    -   a first insulating layer disposed on the first thermoelectric        conversion module; and    -   a second thermoelectric conversion module disposed on the first        insulating layer,    -   wherein the first thermoelectric conversion module includes at        least one thermoelectric conversion element, a first connection        electrode, and a second connection electrode,    -   wherein the at least one thermoelectric conversion element of        the first thermoelectric conversion module is electrically        connected to the first connection electrode and the second        connection electrode and located on an electric path connecting        the first connection electrode and the second connection        electrode,    -   wherein the second thermoelectric conversion module includes at        least one thermoelectric conversion element, a third connection        electrode, and a fourth connection electrode,    -   wherein the at least one thermoelectric conversion element of        the second thermoelectric conversion module is electrically        connected to the third connection electrode and the fourth        connection electrode and located on an electric path connecting        the third connection electrode and the fourth connection        electrode,    -   wherein each of the at least one thermoelectric conversion        element of the first thermoelectric conversion module and the at        least one thermoelectric conversion element of the second        thermoelectric conversion module includes a thermoelectric        converter,    -   wherein the thermoelectric converter includes a phononic crystal        layer having a phononic crystal structure including a plurality        of regularly arranged through holes, and    -   wherein a through direction of the plurality of through holes is        substantially parallel to a stacking direction of the first        thermoelectric conversion module, the first insulating layer,        and the second thermoelectric conversion module.

(Item 2)

The thermoelectric conversion device according to Item 1, wherein the atleast one thermoelectric conversion element of the first thermoelectricconversion module includes two or more thermoelectric conversionelements.

(Item 3)

The thermoelectric conversion device according to Item 1, wherein the atleast one thermoelectric conversion element of the second thermoelectricconversion module includes two or more thermoelectric conversionelements.

(Item 4)

The thermoelectric conversion device according to Item 2, wherein thetwo or more thermoelectric conversion elements are electricallyconnected in series between the first connection electrode and thesecond connection electrode.

(Item 5)

The thermoelectric conversion device according to Item 3, wherein thetwo or more thermoelectric conversion elements are electricallyconnected in series between the third connection electrode and thefourth connection electrode.

(Item 6)

The thermoelectric conversion device according to any one of Items 1 to5, wherein the at least one thermoelectric conversion element of atleast one thermoelectric conversion module selected from the groupconsisting of the first thermoelectric conversion module and the secondthermoelectric conversion module includes:

-   -   a p-type thermoelectric converter;    -   an n-type thermoelectric converter;    -   a first electrode;    -   a second electrode; and    -   a third electrode,    -   wherein the thermoelectric converter includes the p-type        thermoelectric converter and the n-type thermoelectric        converter,    -   wherein a first end of the p-type thermoelectric converter and a        first end of the n-type thermoelectric converter are        electrically connected to each other through the first        electrode,    -   wherein a second end of the p-type thermoelectric converter is        electrically connected to the second electrode,    -   wherein a second end of the n-type thermoelectric converter is        electrically connected to the third electrode,    -   wherein one selected from the second electrode and the third        electrode is disposed on the electric path and located on an        upstream side therein, and    -   wherein the other selected from the second electrode and the        third electrode is disposed on the electric path and located on        a downstream side therein.

(Item 7)

The thermoelectric conversion device according to any one of Items 1 to5, wherein the at least one thermoelectric conversion element of atleast one thermoelectric conversion module selected from the groupconsisting of the first thermoelectric conversion module and the secondthermoelectric conversion module includes:

-   -   two p-type thermoelectric converters adjacent to each other;    -   a fourth electrode;    -   a fifth electrode; and    -   a sixth electrode,    -   wherein the thermoelectric converter includes the two p-type        thermoelectric converters,    -   wherein a first end of a first one of the thermoelectric        converters and a first end of a second one of the thermoelectric        converters are electrically connected to each other through the        fourth electrode,    -   wherein a second end of the first one of the thermoelectric        converters is electrically connected to the fifth electrode,    -   wherein a second end of the second one of the thermoelectric        converters is electrically connected to the sixth electrode,    -   wherein one selected from the fifth electrode and the sixth        electrode is disposed on the electric path and located on an        upstream side therein,    -   wherein the other selected from the fifth electrode and the        sixth electrode is disposed on the electric path and located on        a downstream side therein, and    -   wherein, when an electric current is caused to flow through the        electric path, the directions of the electrode current flowing        through the two adjacent thermoelectric converters are the same.

(Item 8)

The thermoelectric conversion device according to any one of Items 1 to5, wherein the at least one thermoelectric conversion element of atleast one thermoelectric conversion module selected from the groupconsisting of the first thermoelectric conversion module and the secondthermoelectric conversion module includes:

-   -   two n-type thermoelectric converters adjacent to each other;    -   a fourth electrode;    -   a fifth electrode; and    -   a sixth electrode,    -   wherein the thermoelectric converter includes the two n-type        thermoelectric converters,    -   wherein a first end of a first one of the thermoelectric        converters and a first end of a second one of the thermoelectric        converters are electrically connected to each other through the        fourth electrode,    -   wherein a second end of the first one of the thermoelectric        converters is electrically connected to the fifth electrode,    -   wherein a second end of the second one of the thermoelectric        converters is electrically connected to the sixth electrode,    -   wherein one selected from the fifth electrode and the sixth        electrode is disposed on the electric path and located on an        upstream side therein,    -   wherein the other selected from the fifth electrode and the        sixth electrode is disposed on the electric path and located on        a downstream side therein, and    -   wherein, when an electric current is caused to flow through the        electric path, the directions of the electrode current flowing        through the two adjacent thermoelectric converters are the same.

(Item 9)

The thermoelectric conversion device according to any one of Items 1 to8, wherein the phononic crystal layer includes a first phononic crystallayer and a second phononic crystal layer,

-   -   wherein the first phononic crystal layer has a first phononic        crystal structure including a plurality of regularly arranged        first through holes that are part of the through holes,    -   wherein the second phononic crystal layer has a second phononic        crystal structure including a plurality of regularly arranged        second through holes that are part of the through holes, and    -   wherein the first phononic crystal layer and the second phononic        crystal layer are stacked in the stacking direction.

(Item 10)

The thermoelectric conversion device according to Item 9, wherein thefirst phononic crystal layer and the second phononic crystal layer arein contact with each other.

(Item 11)

The thermoelectric conversion device according to Item 9 or 10, whereinat least part of the second through holes are not in communication withthe first through holes.

(Item 12)

The thermoelectric conversion device according to any one of Items 1 to11,wherein the phononic crystal structure has a first domain and asecond domain that are phononic crystal regions,

-   -   wherein the plurality of through holes in the first domain are        arranged regularly in a cross section perpendicular to the        through direction of the through holes, and    -   wherein the plurality of through holes in the second domain are        arranged regularly in a second direction different from the        first direction in the cross section perpendicular to the        through direction of the through holes.

(Item 13)

The thermoelectric conversion device according to any one of Items 1 to12, wherein the phononic crystal layer includes a plurality of pillars,

-   -   wherein the pillars are columnar bodies extending linearly, and    -   wherein each of the pillars is filled into a corresponding one        of the through holes in the phononic crystal layer.

(Item 14)

The thermoelectric conversion device according to Item 13, wherein thephononic crystal layer with the pillars filled thereinto and the pillarsare formed of the same material as each other, and

-   -   wherein a circumferential surface of each of the pillars is        covered with an oxide film.

(Item 15)

The thermoelectric conversion device according to any one of Items 1 to14, further including a temperature detection module.

(Item 16)

The thermoelectric conversion device according to any one of Items 1 to15, further including a control module for controlling a voltage appliedto at least one thermoelectric conversion module selected from the groupconsisting of the first thermoelectric conversion module and the secondthermoelectric conversion module.

(Item 17)

A method for controlling a thermoelectric conversion device, the methodincluding a step of applying a first voltage and a second voltage to thefirst thermoelectric conversion module and the second thermoelectricconversion module, respectively, of the thermoelectric conversion deviceaccording to any one of Items 1 to 16,

-   -   wherein an application pattern of the first voltage differs from        an application pattern of the second voltage.

(Item 18)

The method for controlling according to Item 17, wherein thethermoelectric conversion device includes a first temperature detectionmodule,

wherein the application pattern of at least one voltage selected fromthe group consisting of the first voltage and the second voltage iscontrolled based on information about temperature acquired by the firsttemperature detection module.

(Item 19)

The method for controlling according to Item 17 or 18, wherein an objectto be cooled and/or heated by the thermoelectric conversion device isdisposed near the thermoelectric conversion device.

(Item 20)

The method for controlling according to Item 19, wherein the objectincludes a second temperature detection module, or the secondtemperature detection module is disposed between the object and thethermoelectric conversion device, and

-   -   wherein the application pattern of at least one voltage selected        from the group consisting of the first voltage and the second        voltage is controlled based on information about temperature        acquired by the second temperature detection module.

(Item 21)

The method for controlling according to Item 19 or 20, wherein theapplication pattern of at least one voltage selected from the groupconsisting of the first voltage and the second voltage is controlledsuch that a voltage applied to a thermoelectric conversion module thatis selected from the first thermoelectric conversion module and thesecond thermoelectric conversion module and is located closer to theobject is changed more frequently than a voltage applied to athermoelectric conversion module that is selected from the firstthermoelectric conversion module and the second thermoelectricconversion module and is located farther from the object.

(Item 22)

The method for controlling according to any one of Items 17 to 21,wherein the application pattern of at least one voltage selected fromthe group consisting of the first voltage and the second voltage iscontrolled such that variations in temperature of the object are withina prescribed range.

(Item 23)

The method for controlling according to any one of Items 17 to 22,wherein the object is a heat source.

(Item 24)

A method for cooling and/or heating an object using a thermoelectricconversion device, wherein the thermoelectric conversion device is thethermoelectric conversion device according to any one of Items 1 to 16,

-   -   wherein the method includes a step of applying a first voltage        and a second voltage to the first thermoelectric conversion        module and the second thermoelectric conversion module,        respectively, of the thermoelectric conversion device, and    -   wherein an application pattern of the first voltage differs from        an application pattern of the second voltage.

(Item 25)

An electronic device including:

-   -   an integrated circuit; and    -   a thermoelectric conversion device that cools and/or heats the        integrated circuit,    -   wherein the thermoelectric conversion device is the        thermoelectric conversion device according to any one of Items 1        to 16.

REFERENCE SIGNS LIST

-   1 thermoelectric conversion device-   2 first thermoelectric conversion module-   3 first insulating layer-   4 second thermoelectric conversion module-   5 layered structure-   6 substrate-   7 second insulating layer-   8 protective layer-   9 third thermoelectric conversion module-   10 third insulating layer-   11 first connection electrode-   12 second connection electrode-   13 third connection electrode-   14 fourth connection electrode-   21 thermoelectric conversion element (π type)-   22 p-type thermoelectric converter-   23 n-type thermoelectric converter-   24 first electrode-   25 second electrode-   26 third electrode-   27 insulator-   28 temperature detection module-   31 thermoelectric conversion element (uni-leg type)-   32, 33 thermoelectric converter-   34 fourth electrode-   35 fifth electrode-   36 sixth electrode-   43 first through hole-   44 first phononic crystal layer-   45 second through hole-   46 second phononic crystal layer-   50 through hole-   51A first domain-   51B second domain-   52 phononic polycrystal structure-   53A, 53B orientation-   55 interface-   56 phononic crystal layer-   61 pillar-   62 oxide film-   91, 91A, 91B unit cell

1. A thermoelectric conversion device comprising; a first thermoelectricconversion module; a first insulating layer disposed on the firstthermoelectric conversion module; and a second thermoelectric conversionmodule disposed on the first insulating layer, wherein the firstthermoelectric conversion module comprises one or two or morethermoelectric conversion elements, a first connection electrode, and asecond connection electrode, wherein the thermoelectric conversionelements of the first thermoelectric conversion module are electricallyconnected to the first connection electrode and the second connectionelectrode and located on an electric path connecting the firstconnection electrode and the second connection electrode, wherein thesecond thermoelectric conversion module comprises one or two or morethermoelectric conversion elements, a third connection electrode, and afourth connection electrode, wherein the thermoelectric conversionelements of the second thermoelectric conversion module are electricallyconnected to the third connection electrode and the fourth connectionelectrode and located on an electric path connecting the thirdconnection electrode and the fourth connection electrode, wherein eachof the thermoelectric conversion elements comprises a thermoelectricconverter, wherein the thermoelectric converter of at least one of thethermoelectric conversion elements comprises a phononic crystal layerhaving a phononic crystal structure comprising a plurality of regularlyarranged through holes, and wherein a through direction of the pluralityof through holes in the phononic crystal structure is substantiallyparallel to a stacking direction of the first thermoelectric conversionmodule, the first insulating layer, and the second thermoelectricconversion module.
 2. The thermoelectric conversion device according toclaim 1, wherein the one or two or more thermoelectric conversionelements in the first thermoelectric conversion module comprise two ormore thermoelectric conversion elements; and/or the one or two or morethermoelectric conversion elements in the second thermoelectricconversion module comprise two or more thermoelectric conversionelements.
 3. The thermoelectric conversion device according to claim 1,wherein the thermoelectric conversion device satisfies at least oneselected from the group consisting of the following (a) and (b): (a) theone or two or more thermoelectric conversion elements of the firstthermoelectric conversion module comprise two or more thermoelectricconversion elements, the two or more thermoelectric conversion elementsof the first thermoelectric conversion module being electricallyconnected to each other in series between the first connection electrodeand the second connection electrode; and (b) the one or two or morethermoelectric conversion elements of the second thermoelectricconversion module comprise two or more thermoelectric conversionelements, the two or more thermoelectric conversion elements of thesecond thermoelectric conversion module being electrically connected toeach other in series between the third connection electrode and thefourth connection electrode.
 4. The thermoelectric conversion deviceaccording to claim 1, wherein each of the thermoelectric conversionelements of the first thermoelectric conversion module and/or the secondthermoelectric conversion module comprises: a p-type thermoelectricconverter and an n-type thermoelectric converter, the thermoelectricconverter of the each of the thermoelectric conversion elementscomprising the p-type thermoelectric converter and the n-typethermoelectric converter; a first electrode; a second electrode; and athird electrode, wherein a first end of the p-type thermoelectricconverter and a first end of the n-type thermoelectric converter areelectrically connected to each other through the first electrode,wherein a second end of the p-type thermoelectric converter iselectrically connected to the second electrode, wherein a second end ofthe n-type thermoelectric converter is electrically connected to thethird electrode, wherein one selected from the second electrode and thethird electrode is disposed on the electric path and located on anupstream side therein, and wherein the other selected from the secondelectrode and the third electrode is disposed on the electric path andlocated on a downstream side therein.
 5. The thermoelectric conversiondevice according to claim 1, wherein each of the thermoelectricconversion elements of the first thermoelectric conversion module and/orthe second thermoelectric conversion module comprises: two p-type orn-type thermoelectric converters adjacent to each other, thethermoelectric converter of the each of the thermoelectric conversionelements comprising the two p-type or n-type thermoelectric converters;a fourth electrode; a fifth electrode; and a sixth electrode, wherein afirst end of a first one of the thermoelectric converters and a firstend of a second one of the thermoelectric converters are electricallyconnected to each other through the fourth electrode, wherein a secondend of the first one of the thermoelectric converters is electricallyconnected to the fifth electrode, wherein a second end of the second oneof the thermoelectric converters is electrically connected to the sixthelectrode, wherein one selected from the fifth electrode and the sixthelectrode is disposed on the electric path and located on an upstreamside therein, wherein the other selected from the fifth electrode andthe sixth electrode is disposed on the electric path and located on adownstream side therein, and wherein, when an electric current is causedto flow through the electric path, the directions of the electriccurrent flowing through the two adjacent thermoelectric converters arethe same as each other.
 6. The thermoelectric conversion deviceaccording to claim 1, wherein the phononic crystal layer of thethermoelectric converter of the at least one of the thermoelectricconversion elements comprises a first phononic crystal layer and asecond phononic crystal layer, wherein the first phononic crystal layerincludes a first phononic crystal structure comprising a plurality ofregularly arranged first through holes that are part of the throughholes, wherein the second phononic crystal layer includes a secondphononic crystal structure comprising a plurality of regularly arrangedsecond through holes that are part of the through holes, and wherein thefirst phononic crystal layer and the second phononic crystal layer arestacked in the stacking direction.
 7. The thermoelectric conversiondevice according to claim 6, wherein the first phononic crystal layerand the second phononic crystal layer are in contact with each other. 8.The thermoelectric conversion device according to claim 6, wherein atleast part of the second through holes are not in communication with thefirst through holes.
 9. The thermoelectric conversion device accordingto claim 1, wherein the phononic crystal structure comprises a firstdomain and a second domain that are phononic crystal regions, whereinthe first domain comprises some of the plurality of through holes thatare regularly arranged in a first direction in a cross sectionperpendicular to the through direction of the through holes, and whereinthe second domain comprises some of the plurality of through holes thatare regularly arranged in a second direction different from the firstdirection in the cross section perpendicular to the through direction ofthe through holes.
 10. The thermoelectric conversion device according toclaim 1, wherein the phononic crystal layer comprises a plurality ofpillars, wherein the pillars are columnar bodies extending linearly,wherein each of the pillars is filled into a corresponding one of thethrough holes in the phononic crystal layer, and wherein, when thephononic crystal layer with the pillars filled thereinto and the pillarsare formed of the same material, a circumferential surface of each ofthe pillars is covered with an oxide film.
 11. The thermoelectricconversion device according to claim 1, further comprising a temperaturedetection module.
 12. The thermoelectric conversion device according toclaim 1, further comprising a control module that controls at least onevoltage selected from the group consisting of a voltage applied to thefirst thermoelectric conversion module and a voltage applied to thesecond thermoelectric conversion module.
 13. A method for controlling athermoelectric conversion device, the method comprising a step ofapplying a first voltage to the first thermoelectric conversion moduleof the thermoelectric conversion device according to claim 1 andapplying a second voltage to the second thermoelectric conversionmodule, wherein an application pattern of the first voltage differs froman application pattern of the second voltage.
 14. The method forcontrolling according to claim 13, wherein the thermoelectric conversiondevice comprises a first temperature detection module, and wherein atleast one application pattern selected from the group consisting of theapplication pattern of the first voltage and the application pattern ofthe second voltage is controlled based on information about temperatureacquired by the first temperature detection module.
 15. The method forcontrolling according to claim 13, wherein an object to be cooled and/orheated by the thermoelectric conversion device is disposed near thethermoelectric conversion device.
 16. The method for controllingaccording to claim 15, wherein the object comprises a second temperaturedetection module, or the second temperature detection module is disposedbetween the object and the thermoelectric conversion device, and whereinat least one application pattern selected from the group consisting ofthe application pattern of the first voltage and the application patternof the second voltage is controlled based on information abouttemperature acquired by the second temperature detection module.
 17. Themethod for controlling according to claim 15, wherein at least oneapplication pattern selected from the group consisting of theapplication pattern of the first voltage and the application pattern ofthe second voltage is controlled such that a voltage applied to athermoelectric conversion module that is selected from the firstthermoelectric conversion module and the second thermoelectricconversion module and is located closer to the object is changed morefrequently than a voltage applied to a thermoelectric conversion modulethat is selected from the first thermoelectric conversion module and thesecond thermoelectric conversion module and is located farther from theobject.
 18. The method for controlling according to claim 15, wherein atleast one application pattern selected from the group consisting of theapplication pattern of the first voltage and the application pattern ofthe second voltage is controlled such that variations in temperature ofthe object are within a prescribed range.
 19. The method for controllingaccording to claim 15, wherein the object is a heat source.
 20. A methodfor cooling and/or heating an object using a thermoelectric conversiondevice, wherein the thermoelectric conversion device is thethermoelectric conversion device according to claim 1, wherein themethod comprises a step of applying a first voltage to the firstthermoelectric conversion module of the thermoelectric conversion deviceand applying a second voltage to the second thermoelectric conversionmodule, and wherein an application pattern of the first voltage differsfrom an application pattern of the second voltage.
 21. An electronicdevice comprising: an integrated circuit; and a thermoelectricconversion device that cools and/or heats the integrated circuit,wherein the thermoelectric conversion device is the thermoelectricconversion device according to claim 1.